Aircraft: LARGE TRANSPORT
Phase of flight: Climb
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown

I was scheduled to operate [a] flight to SFO. I arrived at the flight planning area at approximately sunrise. I proceeded to upload and review all applicable flight papers and weather information. By all appearances; it would be an uneventful flight with adequate fuel and no significant weather other than chance of light chop first hour of flight and possible morning cloudiness in SFO. I signed the release and headed toward the gate for the departure. Upon gate arrival; I was cleared out to the jetway and entered the cockpit after introducing myself to the two forward flight attendants. The First Officer; whom I have worked with before; offered a friendly greeting as I stored my bags/equipment. I then briefed with the Lead Flight Attendant (FA) on standard items concerning the flight. After settling in; I asked the First Officer if he had reviewed the flight information and if he had any issues or concerns. He indicated it all looked good to him. I continued with my cockpit setup; to include verification of all installed FMC data. Approximately 20 mins prior to scheduled departure I started the APU as it appeared CS was winding down the boarding process. I transferred electrical to the APU; and after a minute or two; called for the packs to be turned on. Shortly thereafter; I initiated the preflight briefing; concluding with the Preflight Checklist. At departure time; the final door was closed; the Lead FA indicated cabin ready and closed the cockpit door. To this point; no weights had been received; although we had obtained preliminary T/O data for 28. I called for the Before Pushback Checklist and it was completed. The push crew advised that they were ready for push and I asked the First Officer to request push clearance. We received push clearance; I released the brakes; and advised the push crew of the same. At this time; the push crew announced that a late bag had just arrived; and if it was ok to put it on. I advised them to load the bag. After 20 seconds or so; he indicated ready to continue push again and we completed the push process normally. We completed after start flows and After Start Checklist. Taxi to B South was our clearance from Ramp Control. We advised Ground Metering of our position and were instructed to monitor Ground Control. We received clearance to taxi to 28. Shortly after approaching the left turn onto B; Ground Control added follow the air carrier aircraft turning onto B. We acknowledged; and assumed that aircraft would be leading us on our cleared route. To our surprise; the aircraft continued on A10 to T. We queried ATC as to what we were to do and they replied just follow the aircraft. We complied. At this point; we received final weights and printed them out. We did not however receive a 'load' prompt to input the weights data into FMC. We were approximately number 5 for takeoff. The First Officer then requested final weights again. We received weights again; but still no 'load' prompt. The First Officer then proceeded to manually install final weight data and request take off data. We received take off data and installed data manually as we did not receive 'accept' prompt. Now number 2 for departure; we discussed the need for additional time from ATC as we were not ready for departure. We were cleared to the 28 hold pad and to expect full length 28 and to advise ready. At this point we requested takeoff data for full length and proceeded to hold pad. Once in the pad; I made an announcement that we were experiencing a slight delay do to awaiting performance information. The First Officer called dispatch and asked him to resend all pertinent weight and take off data for full length 28 in hopes of getting both the necessary prompts to upload the data automatically. Again we received the relevant data; but still no prompts. We manually reinstalled data; but had no trim setting. The First Officer then called dispatch and obtained the calculated trim setting. Once installed; we felt ready for departure; completed Before Take Off checklist and advised ATC ready. We were in the pad for approximately 10 minutes. We were cleared for takeoff approximately 38 minutes after pushback. The First Officer was the pilot flying. Within 2 or 3 minutes; on initial climb out; we started receiving a stream of multiple data uplinks including performance; winds; and takeoff. I proceeded to 'load' and 'execute' or 'accept' each uplink. This action had a pronounced effect on VNAV and LNAV. The First Officer continued to hand fly using LVL CHG and HDG. Passing 9;000 feet; we were cleared to 15;000 feet; normal speed after 10;000 ft. Approximately 5 minutes after takeoff; passing 12;500 feet; we heard the Cabin Altitude Warning horn and illuminated light. I glanced up at the cabin altimeter and noticed the cabin was indeed at approximately 10;000 ft. As the First officer was starting to level off; we proceeded to extract and don the oxygen masks. I alerted ATC that we were experiencing a cabin altitude issue and requested descent back to 10;000 ft. He cleared us to 10;000 feet and asked if we were declaring an emergency. I acknowledged not at this time; but would evaluate after some investigation and advise. Another glance at the pressurization panel indicated a nominal cabin descent and approximately 1 PSID. I then looked at the air conditioning panel. To my horror; I observed the No. 1 and No. 2 bleed switches in the 'off' position. I pointed to them and confirmed with the First Officer that they should be 'on'; to which he agreed. I positioned them to 'on'. By this time we were leveling at 10;000 ft. The Cabin Altitude Warning horn and associated light went off. Oxygen masks were removed. The Cabin was descending appropriately and the PSID was building commensurately. We assessed the current situation and mutually agreed that this episode had been self-induced; that the cabin altitude was now under automatic control; and that the FMC and MCP functions were all normal. It was decided to continue; so we advised ATC we were ready to continue climb. We were re-cleared to 15;000 feet and proceeded on to SFO with no further anomalies. Since this event occurred; the First Officer and I have had ample time to consider and discuss the likely reasons for missing such an obvious and potentially dangerous omission. Topics including early showtime/departure; distraction from a myriad of taxi out and initial climb issues; and lack of checklist discipline were all mentioned. Personally; not having worked for almost 2 weeks prior to this flight; I might not have been as sharp as I could have been. Perhaps a combination of all these concepts contributed to this event. It reminds us to be ever vigilant and stay focused on the task at hand. A B737NG crew departed with the engine bleed switches OFF. Climbing through 12;500 feet the Cabin Altitude Warning horn sounded. The crew quickly identified the bleeds off condition; the corrected the error; continued the climb and proceeded to their destination.